This invention relates to methods compositions, and apparatuses for improving the effectiveness of froth flotation separation processes. Froth flotation separation is a technique commonly used in the mining industry for separating various mineral constituents from ores. Examples of this method are described in U.S. Pat. No. 6,827,220, in textbook chapters: 12 of Mineral Processing Technology, 6th Edition, by Barry A. Wills, (Published by Butterworth Heinemann), (2003) and 9 of The Chemistry of Gold Extraction, 2nd Edition, by John Marsden and C. Iain House, (Published by SME), (2006), and in the scientific papers: Industrial experiences in the evaluation of various flotation reagent schemes for the recovery of gold, by R. R. Klimpel, Minerals & Metallurgical Processing, Vol. 16 No. 1 (1999) and The Flotation of Gold Bearing Ores—A Review, by C. T. Connor and R. C. Dunne, Minerals Engineering, Vol. 7 No. 7 (1994).
In preparation for flotation, the ore is comminuted (ground up by such techniques as dry-grinding, wet-grinding, and the like) and then dispersed in water to form a suspension known as pulp. Additives such as collectors are normally added to the ore bearing suspension, frequently in conjunction with frothers and optionally other auxiliary reagents such as regulators, depressors (deactivators) and/or activators, in order to enhance the selectivity of the flotation step and facilitate the separation of the valuable mineral constituent(s) from the unwanted gangue constituents. The pulp is conditioned by these reagents for a period of time before a gas, typically air, is sparged into the suspension to produce bubbles of the gas. Minerals that adhere to the bubbles as they rise to the surface are thereby concentrated in the froth that accumulates at the surface of the aerated pulp. The mineral-bearing froth is skimmed or otherwise removed from the surface and processed further to obtain the desired minerals.
The beneficiation of ores by froth flotation utilizes differences in hydrophobicity of various components of a suspension, and these differences in hydrobphobicity may be increased or decreased by judicious choice of chemical additives. In one form, the collector is a hydrophobic agent, which is selectively engaged to the surface of a particular ore constituent and increases the hydrophobicity of the mineral. Gas bubbles admitted during the aeration step will preferentially adhere to the hydrophobicized mineral constituent. Because the mineral components have been treated or modified with the collector, they exhibit sufficiently increased hydrophobicity to be more readily removed from the aerated pulp by the bubbles than are other constituents which are less hydrophobic or hydrophilic. As a result, the collector efficiently pulls the particular ore constituent out of the aqueous solution while the remaining constituents of the ore, which are not modified by the collector, remain suspended in the aqueous phase. This process can also or instead utilize chemicals, which increase the hydrophilic properties of materials selected to remain suspended within the aqueous phase.
In direct flotation processes, the desired mineral which is concentrated and enriched in the froth at the surface of the flotation cell is referred to as the concentrate. The portion of the suspension that does not float is comprised predominantly of gangue minerals of the ore and is referred to as the tails. These tails are often discarded as mine tailings. In reverse flotation processes, the gangue constituent is floated into the concentrate and the desired constituent remains suspended in the slurry. In either type of flotation process, the object of the flotation is to separate and recover as much of the valuable mineral constituent(s) of the ore as possible in as high a concentration as possible which is then made available for further downstream processing steps such as thickening, filtration, and roasting.
A number of materials are known to be useful in facilitating froth flotation separation processes. Collectors based on fatty acids have long been used in collecting one or more of the oxide minerals such as fluorspar, iron, chromite, scheelite, CaCO3, Mg CO3, apatite, or ilmenite. Neutralized fatty acids are soaps that have been shown to operate as non-selective flotation collectors. Petroleum-based oily compounds such as diesel fuels, decant oils, and light cycle oils, are often used to float molybdenite.
Of particular interest to the mining industry are collectors especially effective at selectively floating sulfide mineral ore constituents which comprise complexes with valuable metals including gold, silver, copper, lead, zinc, molybdenum, nickel, platinum, palladium, and other metals. U.S. Pat. No. 7,553,984 teaches that organic molecules containing sulfur are useful compounds for the froth flotation of sulfide minerals.
Organic compounds containing sulfur, such as xanthates, xanthogen formates, thionocarbamates, dithiophosphates, and mercaptans, will selectively collect one or more sulfide minerals such as chalcocite, chalcopyrite, galena, or sphalerite. Such sulfur-based collectors are usually grouped into two categories: water-soluble and oily (i.e., hydrophobic) collectors. Water-soluble collectors such as xanthates, sodium salts of dithiophosphates, and mercaptobenzothiazole have good solubility in water (at least 50 gram per liter) and very little solubility in alkanes. Oily collectors, such as zinc salts of dithiophosphates, thionocarbamates, mercaptans, xanthogen formates, and ethyl octylsulfide, have negligible solubility in water and generally good solubility in alkanes.
Currently used collectors for most sulfide minerals are sulfur-based chemicals such as xanthates, xanthogen formates, thionocarbamates, dithiophosphates, or mercaptans. All of these prior art methods however do not provide optimal recovery rates of the desired minerals and thus there remains a need for improved methods, compositions, and apparatuses for the selective flotation collection of sulfide minerals.